A turbojet with a front fan comprises a large-diameter fan rotor housed in a casing onto which the air intake duct is mounted. An intermediate casing is placed immediately behind the fan casing. Downstream, the hub of the casing is extended by the casing of the main flow and consists of various compressor, combustion chamber, turbine and exhaust casings. The air entering via the air intake duct is compressed through the fan rotor then divided into two concentric cylindrical flows: a main flow and a bypass flow. The latter bypasses the engine and is discharged cold either in a separate flow or, after mixing with the main flow, downstream of the turbine stages. The main flow sustains an additional compression before being mixed with a fuel to produce hot gases in a combustion chamber. The hot gases supply the successive turbine stages which rotate the fan and the air compression stages about the axis of the engine. The main flow is then discharged to supply a portion of the thrust. The latter is produced mostly by the bypass flow. The ratio of the flow rates between the bypass and main flows is called the bypass ratio; the increase in engine power is bringing about the design of engines with a high bypass ratio for which the diameter ratio between the fan casing and the main flow casing is high.